It is well known that X-rays are capable of penetrating substances, and different substances absorb X-rays to different degrees. With the penetrating characteristic and fluorescent characteristic, X-rays may be used to detect an internal structure of an object. Currently, in practice, X-ray detection technologies commonly use film-based photography. Film-based photography offers high imaging quality, and can provide reliable information about a real situation of defects in the object under test correctly. However, it has disadvantages of complex operation process, high running cost, difficulty in storing results and inconvenience to query and carrying.
To solve the above problems, in the 1990s, an X-ray digital radiography detection technology was developed. The basic principle of the X-ray digital radiography technology is using a flat panel detector based on amorphous materials. The flat panel detector is formed by a scintillator (mostly adopting cesium iodide or phosphor), a thin film photodiode array and a thin film transistor array. After an incident X-ray reaches and is absorbed by the scintillator, a visible light is excited and transmitted to a photodiode at a lower layer, converted into an electrical signal, which is integrated in the thin film transistor to become stored charges, and the stored charges are transmitted to a peripheral circuit in sequence as triggered by a control circuit, subjected to amplifying processing by an amplifier after data readout, and converted into a binary digital signal, which is transmitted to and displayed on a console through a cable. As images of an X-ray digital radiography system are formed by digital pixels, and have advantages of high spatial resolution, high image fidelity and large black and white dynamic range, almost the same imaging quality and resolution as that of film-based photography can be achieved, and meanwhile, processing of the images using a computer is facilitated.
The X-ray digital radiography system based on the flat panel detector has a broad vista of applications in nondestructive inspection and evaluation, container scanning, circuit board inspection, and medical applications. Chinese Patent (or Patent Application) Nos. 200580002226.4, 03111635.3, 200710152862.6, 200680016705.6, 200710000874.7, 200610025391.8 and 200810176704.9 introduce wide application of X-rays in medical imaging, nondestructive inspection of industrial products, structural detection of a living body, and safety inspection respectively. As for this, reference may be made to application documents of the patents (or patent applications), which will not be detailed herein.
In the X-ray digital radiography technology, the primary technical difficulty is the process of obtaining an image from the thin film transistor array. This process is a process reverse to the imaging principle of a liquid crystal display (LCD). The technical problem to be solved is to adopt a reasonable combination of thin film transistor structures to convert a visible light image into an electrical signal and implement image reconstruction. Currently, there are various technical solutions to imaging, such as linear scanning; however, such existing technologies still have defects of too long exposure time and low spatial resolution.